Three-dimensional integration (3D-IC) is a solution for improving chip performance while keeping the current technology nodes, and it has many advantages. For instance, functions of a chip can be greatly improved without changing the size of the chip or limited by the manufacturing process of a single chip; metal interconnections between the chips can be highly shortened, so that heat generation, power consumption and delays are reduced; and a band width between functional modules can be greatly enhanced, for example, when a processor chip and a memory chip are subjected to three-dimension integration, the resulted processor can have an ultra-high speed buffer memory.
The existing 3D-IC technology is able to integrate two different chips through through-silicon via or mixed bonding, and can achieve integration and improve device performance. However, along with development of science and technology, higher and higher requirements for device performance and integration degree are raised, and the integration of two layers of chips cannot meet the requirements any more, so it is necessary to develop new technology for the integration of three or more chips.